Optical probe microscope having a fiber optic tip that receives both a dither motion and a scanning motion, for nondestructive metrology of large sample surfaces

ABSTRACT

An optical probe microscope includes an optical fiber oriented in a vertical direction. The fiber has a tip that emits light onto a horizontal surface of a sample to be measured. This surface can have both desired and undesired departures from planarity. An electromechanical device for imparting dither motion to the fiber tip is superposed on another electromechanical device for imparting two-dimensional horizontal scanning motion to the fiber tip. The dither motion has a much higher frequency than that of the scanning motion. Between successive scannings, another device moves the sample itself from one horizontal position to another. A microscope receives the optical radiation either transmitted or reflected by the sample surface. The microscope forms a (magnified) image of this received optical radiation on the surface of an optical image position detector. The surface of this detector has a relatively large area compared with that of the (magnified) image. The resulting electrical signal developed by the detector provides desired information concerning the scanning position of the fiber tip. Also, this electrical signal is processed and fed back to a vertical pusher that maintains desirably constant the distance of the fiber tip from the sample surface.

This application is a continuation of application Ser. No. 08/328,297,filed on Oct. 24, 1994, now abandoned.

FIELD OF INVENTION

This invention relates to optical probe microscopes and to methods ofusing them for metrology of surfaces.

BACKGROUND OF INVENTION

Optical probe microscopes are useful in such applications as measuringboth the heights of, and the lateral extents between, tiny featureslocated on the surfaces of sample bodies. These sample bodies(hereinafter called simply "samples") typically take the form ofsemiconductor wafers (from which many chips are typically subseqentlycut). They also take the form of lithographic masks that are used todefine features on such wafers, including such features as transistorsas well as wiring lines that electrically connect the transistorstogether. Typically the width of such features can be less thanapproximately 0.5 μm, whereas the width of the surface of the wafer orof the lithographic mask can be more than approximately 20 cm. Becausesuch surfaces are not necessarily perfectly smooth (planar) but can haveboth desired features and unwanted bumps, it is desirable to determineboth the heights and widths of the features, as well as the degree ofdeparture of such surfaces from perfect smoothness caused by the bumps.Moreover, unavoidable variations in processing parameters duringfabrication of the features results in unwanted variations in thelateral dimensions of the features. Therefore, it is also desirable tobe able to determine the degree of departure of the lateral dimensionsof the features from the desired values. In other words, it is desirableto be able to determine the topography of the sample surface withsufficient precision. Moreover it is desirable to be able to do sonondestructively--i.e., without destroying the features.

The surfaces of these sample bodies are sometimes referred to as "majorsurfaces" of the sample, because the samples under considerationtypically have a pair of opposed such surfaces, with linear dimensionsof typically more than 20 cm×20 cm, separated by a relatively smallfixed distance s. Typically this fixed distance of separation s ischosen to be in the approximate range of 0.1 mm to 10 mm.

For the sake of definiteness, the direction parallel to such majorsurfaces will be denoted by either the "lateral" direction, the"tangential" direction, or the "horizontal" direction; whereas thedirection perpendicular to such major surfaces will be denoted by eitherthe "normal" direction or the "vertical" direction.

A probe apparatus involving shear force sensing (SFS) can be used todetermine the features and bumps of a sample surface. The apparatusorients the axis of the probe normal to the sample surface. Further, theapparatus imparts a rapid horizontal to-and-fro ("dither") force as wellas a much slower horizontal raster scanning motion to the probe tip.This dither force has a frequency at or near the mechanical resonancefrequency of the probe tip. The resulting amplitude of the dither motionof the probe tip yields desired information concerning the distance ofthe sample surface from the probe tip. Also, the resulting phase of thedither motion relative to the dither force also yields such desiredinformation. Therefore, the apparatus measures either the amplitude orphase of the dither motion, or a combination of both, while the probetip scans the sample surface.

The apparatus used for SFS relies on the fact that, because of the(horizontal) dither motion, shear forces arise in the probe tip that actparallel (rather than normal) to the sample surface. Such shear forcescan arise from static or dynamic friction or from viscous forces in theair (or other fluid medium) located between the probe tip and the samplesurface. These forces change the amplitude and phase of oscillation ofthe vibrating probe tip as it is brought into close proximity to thesample surface. The resulting change in the amplitude or phase of theoscillation, or a resulting change in a combination of both theamplitude and the phase, can then be used to generate a feedback signalfor maintaining constant the probe tip-to-sample surface distance duringscanning. This constant tip-to-surface distance prevents unwantedcollisions between probe and sample, for such collisions can undesirablydestroy the features of the sample surface.

An SFS probe apparatus has omni-directional force sensing capability,that is, the capability of sensing forces not only in the verticaldirection but also attractive and repulsive forces in the horizontaldirection. Therefore, while the probe tip undergoes dither motion, itcan sense both attractive and repulsive forces exerted by sidewalls offeatures. In this way, while the probe tip of an SFS apparatus scans thesample surface, the apparatus can sense the presence of abrupt heightchanges in the sample surface.

An SFS probe apparatus can monitor the dither motion of the probe tip byfocusing a light beam onto the side of the probe at a position of theprobe located in close proximity to the sample surface. Sensing theresulting light intensity scattered from the probe yields a signal thatrepresents the dither motion. For example, one technique for sensing thescattered light intensity involves passing the scattered light through apinhole aperture onto a light detector such as a photo multiplier tube(PMT). Another technique involves detecting the scattered light by meansof a segmented photodiode position sensor that is located at a positionwhere an image of the probe has been focused prior to the existence ofthe dither motion. Both of these techniques sense the dither motion ofthe probe tip. However, relatively large magnifications are required toamplify the dither motion to an extent comparable to the detector'ssensing area, in order to enable proper sensing of the dither motion.These large optical magnifications preclude desired relatively largemechanical translations of the probe tip during scanning: relativelylarge translations of the tip (i.e., on the order of a typical imagescanning-range of several micrometers) will cause the scattered lightarriving at the detector to go outside the light-detecting area, wherebythe light will not be detected. Therefore, except for the dither motionthe probe tip must be held stationary, and the sample (rather than theprobe tip) must be raster-scanned during imaging. Holding the probe tipstationary while thus scanning the sample, however, imposes severe upperlimits on the size of the sample surface that can be inspected.Therefore, full-sized samples such as wafers or masks have to be cutinto small pieces (typically <10 mm×10 mm) to fit on thescanner--typically a piezo fine-scanner. Of course this limitation onsample size is undesirable in the semiconductor industry where thetopography of an entire semiconductor wafer or of an entire lithographicmask must be determined nondestructively.

The teachings of U.S. Pat. No. 5,254,854, alleviate some of theseproblems by means of a shear-force optical microscopy (SFOM) apparatus.Such an apparatus uses optical radiation emitted by the probe tip.However, a problem of limitation on the portion of the sample surfacethat can be inspected by the SFOM apparatus remains.

Apparatus involving a near field scanning optical microscope (NSOM)isanother approach in the art. It can be used in conjunction with SFOM, asthe aforementioned patent teaches. An NSOM apparatus confines theoptical radiation emitted by an optical fiber tip to a relatively smallarea located at the apex of the fiber. In such an apparatus, an opaquelayer typically coats the entire tip of the fiber except at a relativesmall area located at the apex of the fiber tip, whereby the apparatusallows the emission from the fiber tip of only the near-field radiation.The NSOM approach has the advantage of obtaining, with nanometer (0.001μm) resolution, both topographic data of the sample surface andnear-field optical imaging of the sample body simultaneously. Althoughthe aforementioned patent teaches that the NSOM approach can beintegrated into the SFOM apparatus, the problem of limitation on theportion of the sample surface that can be inspected remains

SUMMARY OF INVENTION

In order to ameliorate the aforementioned problems, according to oneembodiment of the invention, an optical probe microscope for inspectinga major surface of a body comprises:

(a) an optical fiber having a tip located in close proximity to themajor surface;

(b) a first electromechanical device, attached to the tip, that canimpart a dither motion to the tip;

(c) a second electromechanical device, attached to the first device,that can impart a scanning motion to the tip, the scanning motion havinga periodicity that is at least approximately 1,000 times as large asthat of the dither motion.

The microscope has omni-directional force sensing capability.Advantageously the optical probe microscope further comprises a thirdelectromechanical device, attached to the first device, that can imparta vertical motion to the tip.

Further advantageously, the optical probe microscope further comprises amicroscope arranged to receive optical radiation emitted by the surfacein response to optical radiation emitted by the tip and incident on thesurface.

Yet further advantageously, the optical probe microscope furthercomprises an optical image position detector, which is arranged toreceive optical radiation from the microscope in response to the opticalradiation received by the microscope, and which develops electricaloutputs, in response to the optical radiation received from themicroscope, that represent the position of the optical radiationreceived from the microscope.

Still further advantageously the optical probe microscope furthercomprises electronic processing circuitry arranged to receive theelectrical outputs of the optical image position detector and to developelectrical outputs that represent the scanning position and the ditherposition of the tip of the fiber.

Still further advantageously, the optical probe microscope furtherincludes feedback circuitry connected to receive an output from theelectronic processing circuitry and to deliver a feedback signal to thethird electromechanical device, whereby the tip of the fiber ismaintained at a constant distance from the major surface of the body.

Still further advantageously, the optical probe microscope furtherincludes a mechanism that can impart horizontal displacements to thebody.

In a second embodiment, the invention involves a method ofmetrologically inspecting a major surface of a body, using an opticalfiber having a tip, comprising the steps of:

(a) directing optical radiation from the tip to the major surface of thebody;

(b) imparting a dither motion to the tip during step (a) by means of afirst electromechanical device attached to the tip;

(c) imparting a scanning motion to the tip during steps (a) and (b) bymeans of a second electromechanical device attached to the first device,the scanning motion having a periodicity that is at least approximately100 times as large as that of the dither motion.

Advantageously the method further comprises the step of impartingvertical motions to the tip during steps (a), (b), and (c) by means of athird electromechanical device.

Further advantageously, the method further comprises

(d) the step of detecting the position of optical radiation coming fromthe major surface of the body in response to step (a); and

(e) developing electrical outputs representing the position.

Advantageously further, the method further comprises electricallyprocessing the electrical outputs of step (e) and developing electricaloutputs that represent the scanning position and the dither position ofthe tip of the fiber.

Advantageously still further, the method further comprises developingand feeding back an electrical feedback signal, representing thedeviation of the distance between the tip and the major surface from aconstant value, to the third electromechanical device, whereby thedistance between the tip and the major surface is restored to theconstant value.

In a third embodiment, the invention involves a method of manufacturingan article comprising the steps of:

(a) providing a plurality of semiconductor bodies, each having a surfaceto be patterned;

(b) setting at least one process parameter;

(c) processing at least a first semiconductor body according to theprocess parameter such that a pattern is formed on the surface of thesemiconductor body, the pattern having a characteristic dimension;

(d) measuring the characteristic dimension in the first semiconductor;

(e) comparing the characteristic dimension to a predetermined range ofvalues;

(f) if the characteristic dimension lies outside the predetermined rangeof values, changing the process parameter to bring the characteristicdimension within the predetermined range of values;

(g) after step (f), processing at least a second semiconductor body inaccordance with the process parameter; and

(h) performing, on at least the second semiconductor body, at least oneadditional step toward completion of the article, characterized in that

step (d) is performed in accordance with the steps recited in the secondembodiment.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevational schematic diagram, partly in cross section, ofan optical probe microscope including fine scanning and coarsepositioning apparatus, in accordance with a specific embodiment of theinvention;

FIG. 2A is an elevational schematic diagram, partly in cross section,showing in greater detail the horizontal fine scanning apparatus of themicroscope shown in FIG. 1;

FIG. 2B is a horizontal cross-sectional diagram of the portion of theapparatus indicated in FIG. 2A;

FIG. 3 is a cross sectional view of an end portion of an optical fiberincluding its tip;

FIG. 4 is an elevational cross-section view of a continuous positionsensor, useful in the practice of the invention;

FIG. 5 is a block diagram of electronic processing circuitry for use inthe practice of the invention in accordance with the specific embodimentthereof; and

FIG. 6 is a block diagram of a specific embodiment of electronicfeedback circuitry for use in the practice of this the invention inaccordance with the specific embodiment thereof.

DETAILED DESCRIPTION

As indicated in FIG. 1, an optical probe microscope 100 includes asample holder system 200 that can horizontally move a sample 35 from onestationary position to another as described in greater detail below. Theprobe microscope arrangement 100 further includes an optical microscope300 and an optical image position detector 400. The optical positiondetector 400 is capable of sensing the position of an optical image,formed on a sensing surface of this detector 400 by the microscope 300.The optical microscope 300 together with the optical image positiondetector 400 form an optical position sensing system 500. In whatfollows the vertical direction will sometimes be denoted by the Zdirection, and the horizontal directions by the X and Y directions, asindicated by the XYZ Cartesian coordinate system shown in FIG. 1.

The sample holder system 200 includes a fine-scanner apparatus 20 thatcan move the tip 14.1 of an optical fiber 14 in either the X or the Ydirection, and a vertical pusher 15 that can move the tip 14.1 of thefiber 14 in the Z direction. For example, the vertical pusher 15comprises a Newport vertical pusher for coarse Z positioning of thesample 35, together with a Burleigh piezoelectric micrometer adapter forfine vertical Z positioning of the sample 35. The tip 14.1 of the fiber14 is described in greater detail in conjunction with the descriptionbelow of FIG. 3.

The sample holder system 200 can further include a conventional opticalmicroscope base and sample stage. For example, the sample holder system200 further includes a supporting base 12, typically a Newport opticsbreadboard having a horizontal cross section of approximately 0.7 m×0.7m. The supporting base 12 is mounted on a vibration isolator 11,typically several layers of damping material such as formed by severalslabs of rubber sandwiched between metal plates.

A coarse XY positioner apparatus is formed in the following manner. Aholder slab 35.4, upon which ball bearings 35.3 can slide with minimalfriction, is supported by posts 39, typically made of quartz or steel.The ball bearings 35.3 are typically made of ruby, but other materialscan be use as known in the art. The ball bearings 35.3 are set inball-bearing holders 35.2, typically made of quartz. In turn, theball-bearing holders 35.2 are fixed, as by an adhesive layer (notshown), to a sample-supporter slab 35.1 upon which the sample 35 isattached. This sample-supporter slab 35.1 is also typically made ofquartz. A metallic position-encoded arm 36 controls the XY position ofthe sample-supporter holder 35 and hence of the sample 35 itself. Thismetallic arm 36 can move the sample-supporter slab 35.1 in the X or Ydirection in increments of typically approximately 0.1 μm. An auxiliaryarm 37 mechanically can move the metallic position-encoded arm 36 inpredetermined encoded increments in the X and Y directions. In turn, arigid sidewall 38 holds the auxiliary arm 37 in place. The posts 39 thussupport the holder slab 35.4 on the supporting base 12, at a fixeddistance apart. The metallic position-encoded arm 36, driven by theauxiliary arm 37, thus forms the basis for the coarse positioning of thesample 35. More specifically, the position-encoded arm 35 moves thesample-supporter slab 35.1, and hence moves the sample 35, in thehorizontal X and Y directions from one (stationary) position to anotheronly at times between completion of each of the (raster) scannings ofrelatively small areas of the sample surface that are described below.More specifically, between such scannings it moves the sample supporterslab 35.1 from one position to another by a distance typically equal toapproximately 20 μm in either the X or the Y direction. In this way,samples 35 having relatively large areas can be inspected: samplesurfaces as large as 20 cm×20 cm, or even more.

During probe measurement operations and as described below in greaterdetail, a laser 13 delivers optical radiation into the fiber 14 throughan optical coupler (not shown). Advantageously the optical radiationpropagating through the fiber is single mode TEoo, for the purpose ofstability of the intensity of the light emitted by the tip 14.1 of thefiber 14.

As indicated in FIG. 2A, top hollow cylinder 31 made of piezo-electricmaterial is glued to the top of the disc 25 by means of adhesive layer18. An insulating disc 27 is glued to the top of the top cylinder 31 bymeans of adhesive layer 19. This disc 27 is typically made of aporcelain or ceramic material.

The disc 27 has an aperture, as shown in greater detail in FIG. 2B. Inthis aperture the fiber 14 is glued to a surface of the glass slab 29.The position of the fiber tip 14.1 is determined and fixed by thepushing of a set screw 28 against an opposed surface of the glass slab29. The purpose of this arrangement shown in the inset is to affordnondestructive precise mounting of the fiber 14.

As indicated in greater detail in FIG. 2A, the fine-scanner apparatus 20includes separate outer electrodes 22 and 23 located on opposite sidesof the outer surface of a bottom hollow cylinder 21 made ofpiezo-electric material. An inner electrode 24 is located everywhere onthe inner surface of the bottom hollow cylinder 21. This cylinder 21 isglued to the top surface of the vertical pusher 15 by means of anadhesive layer 16. The fiber 14 enters into the hollow part of thiscylinder through apertures in the outer electrode 23, the bottomcylinder 21, and the inner electrode 24. An electrically insulating disc(or square) 25 is glued to the top of the cylinder 21 by means ofanother adhesive layer 17. This disc 25 is typically made of a porcelainor ceramic material. The disc 25 has an aperture 26 through which thefiber 14 can fit. The bottom hollow cylinder 21 is much longer (in itsaxial direction) than the top hollow cylinder 31, typically by a factorin the approximate range of 5 to 10 or more. For example, the length ofthe bottom cylinder 21 is approximately 2.5 cm, whereas the length ofthe top cylinder 31 is approximately 0.5 cm. The radius of both top andbottom cylinders is approximately 13 mm. The material of allpiezoelectric layers is typically PZT-5H, while the thicknesses of allpiezoelectric layers is approximately 0.5 mm.

Each of the outer electrodes 22 and 23 subtends an angle of onlyapproximately 90° (=π/2 radian) or less, in order to affect only the Xscanning motion of the tip 14.1 of the fiber 14. The outer electrodes 22and 23, acting in concert with the inner electrode 24, thus can controlthe (raster) scanning movement of the top of the hollow cylinder 21 (andhence of the fiber tip 14.1 ) in the X direction, in response to(raster) scanning voltages δVx and δVx applied to these outerelectrodes. Typically, δVx+=-δVx-, and the periodicity of these voltagesis approximately only 1 sec. Also, typically a voltage bias equal tozero (ground) is applied to the inner electrode 24.

Another pair of outer electrodes (not shown) is located on the outsidesurface of the hollow cylinder 21 in the spaces thereon that are notoccupied by the electrodes 22 and 23. In this way these outer electrodes(not shown) can control the (raster) scanning movement of the top of thehollow cylinder 21 (and hence of the fiber tip 14.1 ) in the Y directionwhen ac voltages (raster) scanning voltages δVy+ and δVy- (not shown)are applied to them. Thus the total number of outer electrodes locatedon the outer surface of the bottom hollow cylinder 21 is four. Typicallythe voltages δVy+ and δVy- have a periodicity of approximately 200 sec.Typically, the maximum displacement of the top of the bottom cylinder 21caused by the voltages δVx+ and δVx- is approximately equal to 20 μm.Hence the maximum horizontal translation in the X or Y direction,respectively, produced by the scanning motion of the fiber tip 14.1 islikewise limited to approximately 20 μm. On the other hand, however,after the voltages δVx+ and δVx- effectuate each such scanning of thesample surface by the fiber tip 14.1, the sample is displaced (movedparallel to itself) horizontally by means of the position-encoded arm 36through a predetermined distance in the X or the Y direction.Accordingly, the ratio of the total linear dimension of the surface ofthe sample 35 that can be inspected (aided by the position-encoded arm36) to the linear dimension of a single scanning of the sample(effectuated by the applied voltages δVx and δδVx, or δVy+ and δVy-) istypically equal to approximately 20 cm ÷20 μm=10,000.

Changing the dc bias applied to the inner electrode 24 enables changingof the vertical position of the top region of the hollow cylinder 21,and hence changing this dc bias enables changing of the verticalposition of the fiber tip 14.1 if desired.

Outer electrodes 32 and 33 are located on opposite sides of the outersurface of the hollow cylinder 31. An inner electrode 34 is locatedeverywhere on the inner surface of the cylinder 31. Each of theelectrodes 32 and 33 subtends an angle of only approximately 90°(=π/2radian) or less, in order to affect only the X dither motion of the tip14.1 of the fiber 14.

As further indicated in FIG. 2A, application to the outer electrodes 32and 33 of applied voltages dVx+ and dVx-, respectively, produces thisdither motion. Since dither motion only in the X direction is required,another pair of outer electrodes located on the outer surface of the tophollow cylinder 21 is not needed. The outer electrodes 32 and 33, actingin combination with the inner electrode 34, thus can control the dithermovement dX of the fiber tip 14.1, in similar fashion as describe abovein connection with the raster scanning of this fiber tip. However, thedither periodicity produced by the voltages dVx+=-dVx is typically muchlower than the scanning periodicity produced by the applied voltagesδVx+ and δVx-.

Typically the frequency of the voltages dVx+=-dVx- is in the approximaterange of 20 kHz to 100 kHz--that is to say, the dither periodicity is inthe approximate range of 0.00005 sec to 0.00001 sec. In any event, thefrequencies of the voltages dVx+=-dVx-, as well as of the voltages δVy+and δVy-, are selected to avoid mechanical resonances of the both theupper and the lower cylinders. The resulting amplitude of the dithermotion is equal to typically approximately 0.05 μm.

As further shown in FIG. 2A, the sample 35 is located between the tip14.1 of the fiber 14 and the microscope 300. This microscope 300typically comprises one or more lenses, arranged to produce a magnifiedimage of the optical radiation arriving from the sample 35 on an opticaldetecting surface of a light image sensor located in the optical imageposition detector 400, as described in greater detail below. The opticalimage position detector 400 has a pair of output terminals 41 and 42.During operations, signals coming from the output terminals 41 and 42yield desired information concerning the instantaneous value of the Xcoordinate of the fiber tip 14.1, also as described in further detailbelow. Similarly, the optical image position detector 400 has anotherpair of output terminals 43 and 44 (not shown in FIG. 2A or FIG. 2B, butshown in FIG. 4) suitable for yielding desired information concerningthe instantaneous value of the Y coordinate of the fiber tip 14.1, alsoas described in further detail below.

FIG. 3 shows the tip 14.1 of the fiber probe 14 in greater detail. Thefiber 14 has a diameter A of typically approximately 125 μm. It also hasa core region 14.2 of diameter a typically equal to approximately 3 μm.The tip 14.1 of the fiber 14 tapers to a diameter b typically equal toapproximately 0.2 μm. The taper is arranged so that the resultingintersection 14.3 of the core region 14.2 with the surface of the fibertip 14.1 is separated by a height h from the extreme apex surface 14.4of the fiber tip 14.1. Typically this height h is equal to approximately5 μm.

During operations, the apex surface 14.4 is maintained at a constantdistance S of separation from the nearest point of the top surface ofthe sample 35, as described in greater detail below. Typically thisdistance S is equal to approximately 0.05 μm.

The microscope 300 in its simplest form (not shown) can take the form ofan objective lens and an eyepiece arranged to produce a real image onthe surface of a continuous position sensor 45 (FIG. 4). In anotherembodiment the microscope comprises four lenses (not shown): anobjective lens that forms a real image on a focal plane of a collimatinglens, an auxiliary lens that forms a real image of the light emergingfrom the auxiliary lens, and another collimating lens having a focalplane locate on the real image formed by the auxiliary lens--whereby thelight emerging from the microscope is in the form of a parallel beam.Typically the magnification of the lens system thus formed in themicroscope 300 is approximately 1,000.

As shown in FIGS. 4 and 5, the optical image position detector 400comprises the continuous position sensor 45 (FIG. 4) plus suitableelectronic processing circuitry 50 (FIG. 5) for converting outputcurrents of this continuous position sensor 45 into output voltagesrepresenting normalized values of the X and Y coordinates (locations) ofthe position of the tip 14.1 of the optical fiber 14. Here the term"normalized" refers to a determination of the values of X and Y that isnot spuriously influenced by fluctuations in the optical intensityproduced by the optical source 13 (FIG. 1 ) or by other fluctuations inthe optical intensity emitted by the tip 14.1 of the fiber 14.

Illustratively, this continuous position sensor 45 comprises asemiconductor PIN-conductivity type structure 46. This structure 46 isformed by a semiconductive silicon bulk region 46.1, having N typeconductivity, into whose bottom surface an N+ type conductivity region46.2 has been diffused and into whose top surface a P+ type conductivityregion 46.3 has been diffused. A protective layer 47, typically ofsilicon dioxide, is located on the top surface of the structure 46. Thisprotective layer 47 is electrically insulating and has an aperture.Thus, light can be incident on the exposed top surface of the P+diffusion region 46.3, as known in the art. Typically the aperture takesthe form of a square, as indicated in FIG. 4.

An electrically conducting layer 48 is located on the bottom surface ofthe structure 46 in electrical contact with the bottom surface of the N+type conductivity region 46.2, as known in the art of semiconductorphotodetectors. The terminals 41,42, 43 (not shown in FIG. 4), and 44are located on the top surface of the P+ region 46.3 at four respectivelocalized areas thereof located (FIG. 4) near the edge of the aperturein the protective layer 47.

As further shown in FIG. 4, light from the microscope 300 is incident onthe top surface of the P+ diffusion region 46.3 to form an image spot 49thereon through the aperture in the protective layer. Advantageously,the lateral dimensions of this spot are much smaller than those of theaperture in the protective layer 47. For example, the aperture in theprotective layer 47 has the form of a square with an area equal toapproximately 10 mm×10 mm, whereas the linear dimension of the imagespot 49 in any direction is in the approximate range of 0.1 mm to 1.0mm. Thus the ratio of any linear dimension of the aperture to that ofthe spot 49 is in the approximate range of at least 10 to 100.

Typically, a negative voltage bias is applied between the P+ diffusionregion 46.3 and the N- bulk region 46.1, during detection of theposition of the image spot 49 by the continuous position sensor 45. Theresulting electrical currents lx+, lx-, ly+, and ly-that arerespectively generated on wires 41.1, 42.1, 43.1 (not shown in FIG. 4)and 44.1 respectively attached to the terminals 41,42, 43, and 44, yieldthe desired information concerning the XY position of the image spot 49on the top surface of the P+ diffusion region 46.3, as known in the art.In particular, the difference (lx+-lx-) between the electrical currentslx+ and lx- is proportional to the X coordinate of the spot 49 measuredfrom the center of the square aperture in the protective layer 47. Thus,lx+-lx-=CΔX, where ΔX denotes μX+dX, as is desired in the practice ofthis invention. Similarly, the difference between ly+ and ly- isproportion to the Y coordinate of the spot 49 measured from the centerof the square aperture in the protective layer 47. Thus, ly+-ly-=CΔY,where ΔY denotes δY+dY, as is also desired in the practice of theinvention. These proportionality relationships assume, of course, thatthe square aperture is symmetrically situated with respect to the activephotodetecting region of the structure 46. It should also be rememberedthat since typically there need be no dither motion in the Y direction,typically dY=0.

As shown in FIG. 5, the four outputs on wires 41.1, 42.1, 43.1, and44.1, generated by the continuous position sensor 45, are fed to apreamplifier 51. Two of the resulting four voltage outputs of thispreamplifier 51--namely, 51.1 and 51.2, proportional to lx+ and lx-,respectively--are fed to a summing amplifier 50 (labeled Σ) and to adifference amplifier 53 (labeled Δx). Another two of the resulting fourvoltage outputs of the preamplifier 51--namely, 51.3 and 51.4,proportional to ly+ and ly-, respectively--are fed to another differenceamplifier 54 (labeled Δy). As used herein, the term "fed" refers to thesituation where the output terminal(s) of one device is (are) connectedto the input terminal(s) of another device, whereby the output signal(s)developed by the one device constitute the input signal(s) to the otherdevice.

The difference amplifier 54 produces an output voltage that isproportional to ly+-ly- and hence to CΔY, and this output voltage is fedto an input terminal of a low pass filter 55 (labeled LPFY). This lowpass filter 55 has an output that is proportional to only the lowfrequency components in the signal fed to it, typically to only thosefrequency components in ΔY that are less than approximately 100 Hz. Theoutput of this low pass filter 55 is fed to the numerator terminal of adivider 56. On the other hand, the output of the summing amplifier 52 isfed to a denominator terminal of the divider 56 (labeled ΔEL/Σ). Thusthe output of the divider 56, which is fed to an output terminal 57.2 ofthe electronic processing circuitry 50, is proportional to ΔEL/Σ, whichis the normalized Y position of the low frequency (i.e., scanning)component of the tip 14.1 of the fiber 14, as is desired. Typicallythere is no dither component in the Y coordinate of the position of thetip 14.1, as mentioned above. Even if there were such dither componentin the Y direction, it would have no influence on the signal appearingat the output terminal 57.2: the low pass filter 55 would not allow anysuch dither (high) frequency components to pass through it.

The normalized X position of the scanning of the tip 14.1 of the fiber14 is determined in a similar manner. More specifically, the output ofthe difference amplifier 53 is fed to a numerator input terminal ofanother divider 59 via another low pass filter 58 (labeled LPFX). Thefrequency pass characteristic of this low pass filter 58 is to that ofthe low pass filter 55 described above. The output of this low passfilter 58 is fed to a numerator input terminal of another divider 59(labeled ΔXL/Σ) to whose denominator input terminal the output of thesumming amplifier 52 is fed. The output of the divider 59 is fed toanother output terminal 57.1 of the electronic processing circuitry 50.Because the high frequency components cannot pass through the low passfilter 58, the dither motion of the tip 14.1 of the fiber 14 has noinfluence on the output of the divider 59. Thus the electrical signalsappearing at both of the output terminals 57.1 and 57.2 of theelectronic processing circuitry 50 are respectively proportional to theX and Y scanning positions (uninfluenced by dither motion) of the tip14.1 of the fiber 14, as is desired in the practice of the invention.

For the purpose of monitoring and controlling the dither motion of thetip of the fiber 14, the output of the difference amplifier 53 is alsofed to an input terminal of a high pass filter 60 (labeled HPF). Thishigh pass filter 60 has an output that is proportional to only highfrequency components of its input, typically to those components higherthan approximately 10 kHz in the case where the frequency of the dithermotion is in the approximate range of 20 kHz to 100 kHz. This output ofthe high pass filter 60 is fed to a numerator input terminal of stillanother divider 61 (labeled ΔXH/Σ) whose denominator input terminal isconnected to the output terminal of the summing amplifier 52. Thus theoutput of the divider 61 is proportional to the normalized high (dither)frequency components of the motion of the tip 14.1 of the fiber 14 inthe X direction. In turn, the output of this divider 61 is fed to anumerator input terminal of yet another divider 62 (labeled ΔXH/ΔXL) towhose denominator input terminal the output of the divider 59 is fed.Thus the output signal 57.3 of the divider 62 is proportional toΔXH/Σ÷ΔXL/Σ=ΔXH÷ΔXL--that is to say, is proportional to the ditherposition divided by the scanning position. The purpose of this divisionby the divider 62 is to normalize the dither position with respect tothe scanning position, in order to correct for nonuniformities in thedetection sensitivity of the surface of the structure 46 of thecontinuous position sensor 45 (FIG. 4) It is desirable that this ratiobe maintained at a constant, predetermined value, in order to maintainthe distance of separation S between the apex surface 14.4 of the fiber14 and the nearest point on the top surface of the sample 35 at aconstant, predetermined value. The feedback circuitry 70 shown in FIG. 6is designed to accomplish this task.

As shown in FIG. 6, the normalized dither signal 57.3 is fed to an inputterminal of a lock-in amplifier 63 (labeled L) that converts thenormalized dither signal 57.3 to a corresponding dc level. Morespecifically, the lock-in amplifier 63 develops an output voltage signal63.1 that has a dc level A that is proportional to the amplitude of thedither motion divided by the amplitude of the raster motion.

Alternatively, this lock-in amplifier 63 is arranged to develop anoutput voltage that is proportional to the sine of the phase shift φ(i.e.,to sin φ) produced by the dither motion relative to the voltagesdVx+ and dVx-applied to the outer electrodes 32 and 33 (FIG. 2A). Asanother alternative, the lock-in amplifier 63 is arranged to develop anoutput voltage that is proportional to A sinφ. At any rate, the outputvoltage signal 63.1 is then fed to the input terminal 71.1 of anotherdifference amplifier 71. This difference amplifier 71 has another inputterminal to which a reference voltage V_(REF) is applied duringoperations. This reference voltage V_(REF) is selected to maintain thedither amplitude of the tip 14.1 of the probe 14 at a desired value. Theoutput of the difference amplifier 71 constitutes an error signal(labeled ε) which is fed to an input terminal of a gain amplifier 72(labeled G). The output of this gain amplifier 72 is fed to anintegrator 73 (labeled ∫). This integrator 73 advantageously has anintegration time constant that is equal to approximately one millisec,that is a time constant that is much larger than the scanningperiodicity but is somewhat less than the dither periodicity. Finally,the output of the integrator 73 is fed to the vertical pusher 15,whereby the vertical pusher 15 moves the fiber 14 in the Z direction insuch a manner as to reduce the error signal ε substantially to zero. Inthis way, the feedback circuitry 70 cooperates with the signal 57.3produced by the electronic processing circuitry 50 to maintain thedither amplitude at a constant value and at the same time also tomaintain the distance of separation S between the apex surface 14.4 ofthe fiber 14 and the nearest point on the top surface of the sample 35at a constant value.

The inventive optical microscope 100 can applied to the field ofmanufacturing devices, such as the field of manufacturing devices bymeans of processes that involve, for example, patterning a surface of asubstrate. Such a a substrate is a pattern of metallic conductors. Thispattern of metallic conductors is formed by deposition of a metalliclayer followed by deposition of a resist layer, selective exposure ofthe resist layer to actinic radiation, development of the resist layerto form a patterned resist layer, and etching the exposed portions ofthe metallic layer (not coated by the thus patterned resist layer) toform elongated metallic conductors. Such processes are characterized byprocess parameters that often must be optimized by trial and error. Oneor more substrates are typically processed in this way for trialpurposes. The pattern, which has been formed on a major surface of sucha substrate according to initial process parameters, is inspected withthe inventive optical probe microscope. During such inspection, thesubstrate together with its pattern of metallic conductors takes theplace of the sample 35 (FIGS. 1 & 2) described above. In this way, oneor more characteristic dimensions on the major surface of the substrate,such as metallic conductor linewidths, are measured, as described above.If the characteristics fail to conform to predetermined desiredspecifications, one or more of the process parameters are modified inorder to bring subsequently processed substrates into conformity withthe specifications.

Although the invention has been described in detail in terms of aspecific embodiment, various modifications can be made without departingfrom the scope of the invention. For example, instead of piezo-electricinduced motions in the top or bottom cylinder, or in both of them, otherforms of induced motions can be used such as motions induced bymagnetic-field-induced actuators, as known in the art. Instead of usingtransmission of light from the tip 14.1 of the fiber 14 through thesample 35 to the microscope 300, the fiber can be positioned in such away that reflection of light from the top surface of the sample 35arrives at the microscope 300.

The invention claimed is:
 1. An optical probe microscope comprising:(a)an optical fiber having a tip placeable in close proximity to a surfaceof a body; (b) a first electromechanical device, attached to the tip,that can impart a dither motion to the tip; (c) a secondelectromechanical device, attached to the first device, that can imparta scanning motion to the tip, the scanning motion having a periodicitythat is at least approximately 100 times as large as that of the dithermotion; (d) a microscope arranged to receive optical radiation emittedby a surface of a body in response to optical radiation emitted by thetip and incident on the surface; and (e) an optical image positiondetector, which is arranged to receive optical radiation from themicroscope in response to the optical radiation received by themicroscope, the optical image position detector having a continuousposition-sensitive photoelectric surface region, the optical radiationbeing focused by the microscope to form an image spot on thephotoelectric surface region, the spot having lateral dimensions thatare less than approximately one-tenth the lateral dimensions of thephotoelectric surface region, whereby the optical image positiondetector develops electrical outputs, in response to the opticalradiation received from the microscope, that represent the position ofthe image spot.
 2. The optical probe microscope of claim 1 in which thespot has lateral dimensions in the approximate range of one-tenth toone-hundredth of the lateral dimensions of the photoelectric surfaceregion.
 3. The optical probe microscope of claim 1 further including amechanism that can impart horizontal displacements to the body, themechanism comprising an arm attached to a slab that can support thebody.
 4. The optical probe microscope of claim 3 further comprisingelectronic processing circuits arranged to receive the electricaloutputs of the optical image position detector and to develop electricaloutputs that represent the scanning position and the dither position ofthe tip of the fiber.
 5. The optical probe microscope of claim 1 furthercomprising a third electromechanical device, attached to the firstdevice, that can impart a vertical motion to the tip.
 6. The opticalprobe microscope of claim 5 in which the spot has lateral dimensions inthe approximate range of one-tenth to one-hundredth of the lateraldimensions of the photoelectric surface region.
 7. The optical probemicroscope of claim 5 further comprises electronic processing circuitryarranged to receive the electrical outputs of the optical image positiondetector and to develop electrical outputs that represent the scanningposition and the dither position of the tip of the fiber.
 8. The opticalprobe microscope of claim 7 further including a mechanism that canimpart horizontal displacements to the body, the mechanism comprising anarm attached to a slab that can support the body.
 9. The optical probemicroscope of claim 7 further including feedback circuitry connected toreceive an output from the electronic processing circuitry and todeliver a feedback signal to the third electromechanical device, wherebythe tip of the fiber is maintained at a constant distance form thesurface of the body.
 10. The optical probe microscope of claim 9 furtherincluding a mechanism that can impart horizontal displacements to thebody, the mechanism comprising an arm attached to a slab that cansupport the body.
 11. A method of metrologically inspecting a majorsurface of a body, using an optical fiber having a tip, comprising thesteps of:(a) placing the tip in close proximity to the major surface anddirecting first optical radiation into the fiber at an end thereofdistal to the tip, whereby optical radiation is incident on the majorsurface of the body; (b) during step (a) applying dither voltages to afirst electromechanical device, attached to the tip, whereby a dithermotion is induced in the tip in response thereto; (c) during step (b)applying scanning voltages to a second electromechanical device,attached to the first electromechanical device, whereby a scanningmotion is induced in the tip in response to the scanning voltages, thescanning motion having a periodicity that is at least approximately1,000 times as large as that of the dither motion; and focusing secondoptical radiation, coming from the body in response to the first opticalradiation, to an optical image spot on a continuous position-sensitivephotoelectric surface having lateral dimensions that are at leastapproximately ten times the lateral dimensions of the optical imagespot.
 12. The method of claim 11 further comprising the step of(d)applying vertical motion voltages to a third electromechanical device,attached to the fiber, whereby vertical motions are induced in the tipduring steps (a), (b), and (c) in response to the vertical motionvoltages.
 13. The method of claim 12 further comprising the steps of(d)detecting the position of optical radiation coming from the majorsurface of the body in response to step (a); and (e) developingelectrical outputs representing the position.
 14. The method of claim 13further comprising electrically processing the electrical outputs ofstep (e) and developing electrical outputs that represent the scanningmotion and the dither motion of the tip of the fiber.
 15. The method ofclaim 14 further comprising developing and feeding back an electricalfeedback signal, representing the deviation of the distance between thetip and the major surface from a constant value, to the thirdelectromechanical device, whereby the distance between the tip and themajor surface is restored to the constant value.